This invention relates to a submersible single phase capacitor-start, induction motor and particularly a capacitor-start induction motor having a capacitor connected in circuit with a start winding only during the starting.
Submersible motors are widely used for pumping of water and other liquids. A significant usage of submersible motor is in domestic deep drilled water wells in which the well is drilled to a depth of hundreds of feet into the ground. A submersible motor-pump unit is supported immersed within the well by the discharge piping. The submersible motor-pump unit includes an elongated motor with a pump unit secured to the upper end thereof. Power lines are dropped down through the well casing and connect the motor to the power supply through a suitable control to provide for selective motor operation and pumping of water from the well. Each time the motor starts, it must operate the pump to initiate flow, lifting the water from the well upwardly through the piping. A relatively heavy starting load is created and the submersible motor must be constructed with a corresponding high starting torque. A well known and convenient method to create high starting torque in a single phase motor is to provide a separate start circuit branch which includes a starting winding in series with a capacitor to establish a phase shifted magnetic field which increases the starting torque. When the motor approaches or reaches operating speed, the torque requirements drop significantly. Conventionally, a speed responsive switch means is provided to disconnect the starting branch circuit and the motor continues to operate as a single phase induction motor.
Various systems have been provided for physically locating the capacitor at the upper end of the well casing or as an integrated part of the motor. If the capacitor is located as an integrated part of the motor, a two-wire supply cable is connected to the motor. If the capacitor is located at the upper end of the well, a three-wire supply cable is required. The motor is preferably constructed to operate as either a two-wire or a three-wire motor unit to permit manufacture and inventory of a single basic design. This of course requires some form of a releasable interconnection of the capacitor to the motor unit. Various suggestions have been made. For example, U.S. Pat. No. 3,604,964 discloses a submersible motor-pump unit having a capacitor releasably mounted within a separate end member attached to the lower end of the motor. The lower end of the motor proper is further provided with a releasable electrical connector having a motor component or part connected to the windings and a separate part connected to leads which extend downwardly and are connected to the inner end of the capacitor. If the motor is to be operated as a two-wire motor, the capacitor is suitably secured to the motor and the two lead wires connected to the upper end of the motor. The two wires supply power to the motor with the internal connections provides for the connection of the capacitor into the circuit. In at least one embodiment, the above patent also suggests a voltage responsive electromagnetic relay be provided within the lower capacitor housing. The relay winding is energized at a predetermined voltage to open the contacts and thereby disconnect the start branch. The opening of the contacts results in arcing which may create various practical adverse effects which prevent commercial implementation. To operate the motor as a three-wire motor, the capacitor unit is disconnected from the motor. A three-wire cable is connected to power and a remote capacitor and to the motor to supply power to the motor and simultaneously provide separate connection of a remotely located capacitor in the start branch. The internal centrifugal switch automatically disconnects the start branch at the appropriate speed as the motor reaches or approaches normal operating speed.
A generally similar system is disclosed in U.S. Pat. No. 3,457,867 wherein the capacitor unit is secured to the lower end of the motor. A separate cable member connects the capacitor unit to a single motor connector at the upper end of the motor for appropriate interconnection to the incoming power supply cable. In this instance, the motor can be operated as a three-wire supply with an external capacitor, in which event the integrated capacitor is not connected to the motor. U.S. Pat. No. 4,297,627 discloses a motor having an internal wired cutout switch unit with an external plug-in connection adapted to receive a capacitor unit to operate as a capacitor-start motor or a shorting plug to operate as a split phase motor. Other patents which similarly show selective connection for two wire or three wire motor operation are shown in the following U.S. Pat. Nos. 2,032,129; 3,248,582; 3,350,585; 3,420,974; 3,457,866; 3,631,275; 3,761,750.
Although the various submersible motor systems have provided satisfactory operating functional and operating characteristics, submersible pump motor units are relatively expensive and have a limited life. Further, the capacitor and switching system may fail and simple replacement of just such components will provide an extended operating life of the submersible motor-pump unit. There is a need therefore for a relatively simple construction of a two/three-wire motor having a reliable switching means and a long life capacitor and switching means.